I. Field of the Invention
The present invention relates to the fields of oncology and molecular biology. More particular the invention relates to cancer therapies utilizing a fragment of adenovirus E1A that represses transcription of oncogenic genes such as HER2/Neu.
II. Related Art
Up-regulation of the HER2/neu (erbB2) proto-oncogene occurs in several types of human cancer, including breast, ovary, and prostate. HER2 up-regulation in breast cancer is predictive of aggressive disease with a poor prognosis; 25-30% of breast cancers are positive for HER2 up-regulation but account for 60-80% of breast cancer deaths (Moasser, 2007a). Of significance, several studies have shown that elevated HER2 levels decrease the susceptibility of cancer cells to chemotherapeutic drugs (Moasser, 2007b). Further, treatment with siRNAs that inhibit HER2 translation was found to promote growth arrest and apoptosis of breast cancer cell lines (Choudhury et al., 2003). These findings appear to be examples of what has been termed “Oncogene Addiction” (Weinstein, 2002).
Several studies with human cancer cell lines have shown that although they may have acquired multiple genetic and epigenetic abnormalities, they can remain highly dependent on the expression of a single oncogene for cell proliferation and survival (Weinstein and Joe, 2008). Oncogene addiction has been demonstrated in several mouse model systems including MYC-driven papillomas, lymphomas and osteosarcomas (Felsher and Bishop, 1999; Jain et al., 2002; Pelengaris et al., 1999), hRAS-driven melanoma (Chin et al., 1999) and BCR/ABL-driven leukemia (Huettner et al., 2000). Interference with the function of the oncogene which drives a specific tumor is a therapeutic approach that has met with some clinical success including targeting BCR-ABL (imatinib), EGRF (gefitinib, erlotinib) and HER2 (trastuzumab) (Weinstein and Joe, 2008).
The Ad group C (types 2 and 5) E1A oncogene encodes two major proteins of 243 and 289 amino acid residues (243R and 289R) which contain multiple functional domains that interact with key cellular regulatory factors. E1A is involved in diverse functions, including transcriptional activation, induction of cellular DNA synthesis, cell immortalization, cell transformation, and of particular interest, transcriptional-repression. E1A 289R differs from E1A 243R by conserved region 3 (CR3), a 46 amino acid domain unique to 289R that is involved in transcription-activation of Ad early genes (Lillie et al., 1987; Green et al., 1988). The Ad5 oncogene inhibits the expression of HER2 in rodent and human cell cultures (Yan et al., 1991; Yu et al., 1990; Yu et al., 1991). However, the full length Ad E1A oncogene is not a good candidate as a therapy because it possesses, in addition to its transcription-repression function, other biological activities which may complicate a medical therapy and could have long-term deleterious effects. Further, other E1A domains interact with several important cellular proteins not associated with its transcriptional repression function, including, for example, Rb, p21, and CtBP, all of which can have profound effects on cell cycle regulation.
The present inventors have previously demonstrated that the transcription-repression function of the E1A oncogene consists of two critical sub-domains that reside solely within the N-terminal 80 amino acids of E1A (Song et al., 1995a; Song et al., 1995b; Song et al., 1995c; Song et al., 1997; Boyd et al., 2002; Loewenstein et al., 2006). Extensive studies demonstrated that the E1A repression domain (a recombinant protein containing only the N-terminal 80 amino acids), exhibits the same repression function as the entire E1A 243R oncoprotein. Single amino acid substitution analysis of the two E1A N-terminal repression sub-domains has led to a two-step model of E1A repression (Boyd et al., 2002; Loewenstein et al., 2006): first E1A gains access to repressible promoters by interaction of E1A repression sub-domains 1 (amino acids—˜1-30) and 2 (amino acids ˜48-60) with a promoter-bound cellular partner such as p300; second, the E1A N-terminus (sub-domain 1) interacts with TBP (TATA binding protein) and disrupts the TBP/TATA complex thus blocking transcription (Green et al., 2008a; Green et al., 2008b). However, the ability of this molecule to repress the expression of oncogenes such as HER2/Neu inside cancer cells has yet to be explored.